The present invention relates to loudspeakers and, in particular, to a flat-panel loudspeaker, preferably used as a compact speaker in a multimedia computer speaker system.
The use of broadband loudspeaker systems with personal computers is gaining popularity. For example, high fidelity sound is desirable with many multimedia computer applications, such as presentations, games, DVD movies and the like. Moreover, as the applications for using a personal computer expand, the need for high fidelity sound with these applications will also increase.
The typical personal computer rests on a desk, and customers expect computer-related peripherals to be relatively inexpensive. Accordingly, it is desirable to make multimedia computer-related loudspeaker systems as compact and economical as possible, but without compromising sound quality.
Thin loudspeakers, commonly referred to as flat panel loudspeakers, have a small profile and can be manufactured inexpensively. One example of such a loudspeaker is found in published PCT patent application serial number WO 99/67974 to Lock et al. (xe2x80x9cLock et al.xe2x80x9d) and titled xe2x80x9cLoudspeakers.xe2x80x9d
In general, the typical flat panel loudspeaker, such as that disclosed in Lock et al., includes at least one substantially planar diaphragm having different flex, or bending strength, characteristics in each of its major axes. The technical term for this characteristic is anisotropic. The diaphragm is secured to a substantially rigid frame defining a narrow chamber therein. A driver, usually centrally aligned with the diaphragm, is operably secured to the diaphragm within the chamber such that upon activation causes the diaphragm to vibrate at desired frequencies, thereby radiating sound therefrom.
In particular, the driver causes various desirable frequency wave patterns to originate in the center of the diaphragm and radiate outward toward the edges of the diaphragm. However, because of the interaction between the diaphragm and frame, upon reaching the substantially rigid frame supporting the diaphragm, many of the wave patterns are reflected back toward the driver along the diaphragm. The reflected waves interfere with the desirable waves emanating from the center of the diaphragm, forming a standing wave of constructive or destructive interference at particular frequencies along the diaphragm. Such interference compromises the quality of sound produced by the loudspeaker. For example, it can amplify the particular frequencies being subjected to the constructive interference by as much as 30 decibels above the other frequency sounds being emitted by the loudspeaker, distorting the overall sound quality of the loudspeaker. This characteristic is especially pronounced when the particular frequencies being subjected to constructive interference are high frequency sounds.
Efforts to reduce undesirable standing waves in flat panel loudspeakers have had limited success. For example, Lock et al. teaches that a dampening cloth may be secured adjacent to the edges to the diaphragm where it contacts the frame. Such a dampener reduces the likelihood of wave patterns from the diaphragm adversely conducting to the frame. However, such materials and their orientation do little to dampen the reflection of high frequency energy back along the diaphragm. Moreover, traditional devices for dampening limited frequency wave patterns, such as using devices to restrict a particular frequency movement of the diaphragm, tend to adversely limit the movement of the diaphragm for both desirable frequency wave patterns within that range and the undesirable reflected wave patterns of the same frequency. Accordingly, such devices adversely compromise the quality of sound generated by the loudspeaker.
The present invention overcomes these and other problems with known flat panel loudspeakers. It is an economical flat panel loudspeaker that has a small profile, but also effectively dampens undesirable standing waves that form in the diaphragm without adversely dampening the frequency response of the diaphragm, thereby providing superior sound quality.
In a preferred embodiment, a substantially planar anisotropic diaphragm and a substantially parallel, spaced-apart planar support are secured to a substantially rigid frame defining a narrow chamber therein. A driver is preferably centrally aligned with the diaphragm and is operably secured between the diaphragm and planar support within the chamber such that activation of the driver causes the diaphragm to vibrate at desired frequencies. At least one compliant dampening member is transposed between the diaphragm and planar support, preferably at or near at least one mode of constructive or destructive interference. The dampening member urges the diaphragm away from the planar support, thereby placing a slight bending force on the diaphragm, and a slight compression force on the dampening member. Accordingly, the dampening member serves as a sink for transferring undesirable standing waves from the diaphragm to the planar support.
More preferably, the dampening member is an elongated strip of compliant foam rigidly secured to the diaphragm and planar support and extending through a plurality of modes of constructive or destructive interference on the diaphragm. In one preferred embodiment, the diaphragm is generally rectangular shaped, and there are a plurality of dampening members forming at least three elongated strips of compliant foam. A first strip of foam is positioned between the driver and the upper edge of the diaphragm, and aligned substantially parallel to the upper edge of the diaphragm. A second strip of foam is positioned between the driver and one of the side edges of the diaphragm and aligned substantially perpendicular to the first strip, and a third strip of foam is positioned between the driver and the opposite side edge of the diaphragm and aligned substantially parallel to the second strip.
In a first alternative preferred embodiment, the first strip has a different compliance than the second and third strips. In a second alternative preferred embodiment, each dampening member has portions of different compliance aligned such that the less compliant (i.e., stiffer) portion is aligned adjacent to the planar support, and the more compliant portion is aligned adjacent to the diaphragm.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.